The alkylation of aromatic compounds such as benzene and benzene derivatives with olefins is carried out on a large scale in the chemical industry (Perego and Ingallina (Catalysis Today (2002) 73:3-22) and Almeida, et al. (JAOCS (1994) 71:675-694). Alkyl benzenes have many industrial uses. For example, ethyl benzene, formed by the reaction of ethylene with benzene, is an intermediate in styrene production. Alkylation of benzene with propylene yields cumene, an intermediate in phenol and acetone production. Linear alkyl benzenes are synthesized from the reaction of longer-chain olefins (ca. 10-18 carbon atoms) with benzene or benzene derivatives; the linear alkyl benzenes are then sulfonated to produce surfactants.
Historically, aromatic alkylation reactions have been carried out in the presence of a homogeneous (i.e., soluble) acid catalyst. One disadvantage to these reactions is the cost associated with separating the catalyst from the reaction product(s). It would be advantageous to carry out the alkylation reaction in such a way that the catalyst could be easily separated from the reaction product(s).
Ionic liquids are liquids composed of ions that are fluid around or below 100 degrees C. (Science (2003) 302:792-793). Ionic liquids exhibit negligible vapor pressure, and with increasing regulatory pressure to limit the use of traditional industrial solvents due to environmental considerations such as volatile emissions and aquifer and drinking water contamination, much research has been devoted to designing ionic liquids that could function as replacements for conventional solvents.
U.S. Pat. No. 5,824,832 provides a process for making a linear alkyl benzene using an ionic liquid as the catalyst.
The present invention provides a process for carrying out aromatic alkylation reactions using ionic liquids as a solvent. The use of ionic liquids as the solvent for this reaction allows for ready separation of the product(s) from the catalyst.